A “MOF-Protective-Pyrolysis” Strategy for the Preparation of Fe–N–C Catalysts and the Role of Fe, N, and C in the Oxygen Reduction Reaction in Acidic Medium

M–N–C electrocatalysts for the oxygen reduction reaction (ORR) have been considered as the most promising alternatives to precious metal catalysts. However, the catalytic activity of M–N–C especially in an acidic medium is still unable to meet the practical requirement, and the corresponding ORR mechanism also remains unclear. Herein, an “MOF-protective-pyrolysis” strategy was adopted to synthesize an Fe–N–C catalyst (P-FeMOF@ZIF-8) with Fe–N4 as the predominant Fe species. The P-FeMOF@ZIF-8 displays high catalytic activity in both acidic and alkaline mediums. The experimental results further reveal the different importance of the Fe species in different mediums. Based on the results, a distinct mechanism of the ORR the in acidic medium was proposed, where the synergistic effect of the Fe–N4 site and carbon in improving the kinetics of the ORR were well explained. The findings and the corresponding perspective may provide a new guidance for the design of highly efficient ORR electrocatalysts.